The present application relates to a method and apparatus utilizing animals for detecting target substances, such as trace particles, odors and vapors. The invention is useful in many applications, for example in detecting explosives, narcotics or other controlled substances, rotten food products, pesticide residues, chemical by-products of medical situations, etc.
Many techniques have been developed for detecting target substances, e.g., as target odors, present at extremely low concentrations, e.g., in the order 1 part per million, or less. Trained canines have probably been used more than any other method for the detection of explosives under real-world conditions. An animal's nose is the best sensor that evolution has to offer, and it competes favorably with man-made detection technologies under many circumstances. At the present time, there is no mechanical device as accurate, fast, sensitive, mobile, flexible and durable as a well-trained dog/handler team.
However, there are a number of disadvantages in using canines as explosive detectors. First and foremost, adequately maintaining a canine operation, especially in the one-handler to-one-dog mode preferred by many law enforcement organizations, is very expensive. Costs include initial acquisition of the animals, training for both the dog and the handler, veterinary and other maintenance expenses for the dogs, and the salary and other expenses associated with the handler, this last constitutes the largest fraction by far.
Thus, explosive sniffer dogs do not, and cannot, operate by themselves. They always function in tandem with their handler. The leash that connects the man and dog is not so much a means of control as a channel for communication. This is both a strength and a weakness. When a team is in top form, the dog and his handler function with amazing efficiency. But the dog works only as well as his master. Security searches are frequently boring, monotonous chores, the sort of tasks for which humans have trouble staying alert. If the dog senses a lack of commitment on the part of his human teammate, the dog's effort similarly diminishes. Also, it is inaccurate to say that the dog finds the explosive. It is up to the handler to recognize the sometimes-subtle changes in the dog's behavior that signal interest in a faint scent. This reliance on the handler's judgment introduces a second possibility of error.
Dogs have a number of weaknesses when compared to mechanical sniffer devices. Being a live creature, dogs cannot be worked as intensely as a piece of machinery. Depending on temperature and humidity conditions, a dog may be able to work only about 20 minutes before he needs a rest. Dogs are also vulnerable to distraction by loud noises, bright lights, new surroundings, fatigue, and alluring scents left behind by canines of the opposite sex. Dogs have a limited attention span. They cannot be positioned beside a conveyor belt, even under comfortable conditions, and be expected to sniff luggage effectively hour after hour. They must be actively engaged in the search, or their acuity will sharply diminish. They also are prone to personality quirks. Some dogs refuse to go in glass elevators; some will not fly in helicopters; some bond very strongly to their handlers, while others are more aloof.
The use of other animals with a developed sense of scent to detect volatile materials is also well known in the art, and is described, among other places in Biederman U.S. Pat. No. 4,022,054.
In most of the methods known in the art, animals are trained by positive reinforcement to actively search for and find the source of the scents typical to the relevant type of material. The animals are then brought to a suspicious place and are instructed to seek the scent, motivated by the expected reward, However, positive reinforcement training and operation carries some inherent limitations that negatively affect their affectivity:
1. The animal will not perform when it is satiated
2. The animal is trained for short term missions and cannot perform continuous monitoring
3. With canines, the operation of the animal typically requires a human trainer or operator and cannot be performed unattended
4. The animal needs frequent training with the target material and reward in order to keep low false alarm rate and high detection rate.
These limitations are problematic both in the operational and in an economical sense.